diff --git a/drivers/spi/spi_b_renesas_ra8.c b/drivers/spi/spi_b_renesas_ra8.c
index 2eb9d79b22d..4d17c9e99f8 100644
--- a/drivers/spi/spi_b_renesas_ra8.c
+++ b/drivers/spi/spi_b_renesas_ra8.c
@@ -86,6 +86,7 @@ static int ra_spi_b_configure(const struct device *dev, const struct spi_config
 {
 	struct ra_spi_data *data = dev->data;
 	fsp_err_t fsp_err;
+	uint8_t word_size = SPI_WORD_SIZE_GET(config->operation);
 
 	if (spi_context_configured(&data->ctx, config)) {
 		/* Nothing to do */
@@ -100,6 +101,11 @@ static int ra_spi_b_configure(const struct device *dev, const struct spi_config
 		return -ENOTSUP;
 	}
 
+	if (word_size < 4 || word_size > 32) {
+		LOG_ERR("Unsupported SPI word size: %u", word_size);
+		return -ENOTSUP;
+	}
+
 	if (config->operation & SPI_OP_MODE_SLAVE) {
 		data->fsp_config.operating_mode = SPI_MODE_SLAVE;
 	} else {
diff --git a/drivers/spi/spi_renesas_ra.c b/drivers/spi/spi_renesas_ra.c
index b19723bdc15..27a25644423 100644
--- a/drivers/spi/spi_renesas_ra.c
+++ b/drivers/spi/spi_renesas_ra.c
@@ -82,6 +82,7 @@ static int ra_spi_configure(const struct device *dev, const struct spi_config *c
 {
 	struct ra_spi_data *data = dev->data;
 	fsp_err_t fsp_err;
+	uint8_t word_size = SPI_WORD_SIZE_GET(config->operation);
 
 	if (spi_context_configured(&data->ctx, config)) {
 		/* Nothing to do */
@@ -96,6 +97,12 @@ static int ra_spi_configure(const struct device *dev, const struct spi_config *c
 		return -ENOTSUP;
 	}
 
+	if (!((word_size >= 8 && word_size <= 16) || word_size == 20 || word_size == 24 ||
+	      word_size == 32)) {
+		LOG_ERR("Unsupported SPI word size: %u", word_size);
+		return -ENOTSUP;
+	}
+
 	if (config->operation & SPI_OP_MODE_SLAVE) {
 		data->fsp_config.operating_mode = SPI_MODE_SLAVE;
 	} else {